1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, the present invention relates to an image forming apparatus having a developing unit comprising a plurality of units.
2. Description of Related Art
General electrophotographic image forming apparatuses such as a laser beam printer, a light emitting diode printer, a facsimile, a digital photocopier and a multi-function office machine print a digital image signal input from a computer or a scanner in the form of a visible image on a printing medium, such as a paper, through a series of image forming processes.
As shown in FIG. 1, an image forming apparatus generally includes a main body 10 having a front door 11, and a developing unit 15 having a photoconductive drum 17 and detachably mounted in a mounting portion 10a. When the developing unit 15 is mounted, the photoconductive drum 17 is mounted to rotate in contact with a transfer roller 14. The transfer roller 14 is supported by a side door unit 12 pivotably mounted at a flank of the main body 10. The side door unit 12 is hinged to open and close the flank side of the main body 10, so as to facilitate removal of a jammed paper and replacement of exhausted parts.
The image forming apparatus operates as follows. The photoconductive drum 17 is uniformly electrified by a developing roller (not shown), and an electrostatic latent image is formed by a light scanned from a laser scanning unit (not shown). A toner is attached onto the electrostatic latent image, thereby forming a visible image. The visible image is transferred to a printing paper which comes from a paper supplying unit 13 and passes through between the transfer roller 14 and the photoconductive drum 17. The printing paper bearing the toner thereon is passed through a fusing unit (not shown) and discharged out to a stacker.
In the general image forming apparatus, for cleaning or fixing of inside of the main body 10, or when the photoconductive drum 17 or the toner is exhausted, the developing unit is replaced as a whole. Such an integral developing unit is usually classified into a uni-structure type wherein all the components such as the photoconductive drum, the developing roller and a toner container are integrally formed, and a dual-structure type has the following two units; a first unit having the toner container and the developing roller; and a second unit having a photoconductive drum 17. FIG. 1 illustrates the latter case of the image forming apparatus in which the developing unit comprises two units. The developing unit 15 of FIG. 1 has a first unit 16 and a second unit 18 mounted in the mounting portion 10a of the main body 10 in complementary connection with each other for the image forming operation.
The first unit 16 has the toner container and the developing roller, and the second unit 18 includes the photoconductive drum 17. During separation of the developing unit 15, the first unit 16 having the developing roller and the toner container is separated first. Since the second unit 18 usually has a life span as about 3 to 4 times as that of the first unit 16 in some image forming apparatuses, the first unit 16 needs to be replaced more frequently.
The developing unit 15 includes the first unit 16 and the second unit 18 should be removed in a specified order. This is because the developing roller (not shown) and the photoconductive drum 17 are so delicate that they can be damaged if removed in a different order. In order to separate the developing unit 15, the front door 11 is open, the first unit 16 having the developing roller (not shown) is drawn first, and then the second unit 18 having the photoconductive drum 17 is drawn out. Otherwise, the parts at the contacting surface of the first unit 16 and the second unit 18 may be damaged while assembling and disassembling. More specifically, since the developing unit 15 is mounted and detached in a length direction thereof, main parts such as the photoconductive drum 17 or the developing roller (not shown) are subject to damage due to the elongated contacting surface between the first and the second units 16 and 18. Further, the first unit 16 is disposed relatively lower than the second unit 18 in the developing unit 15. Therefore, if the first unit 16 is separated first, the second unit 18 can be separated together with the first unit 16, being put on the first unit 16, without problem. However, to separate the second unit 18 first, a user only grips the second unit 18 but does not grip the first unit 16. Since the first and the second units 16 and 18 are not engaged with each other, the first unit 16 may drop to the floor and damaged. Moreover, the toner in the toner container may be leaked out when the first unit 16 drops to the floor.